function equal(a, b) {
    if (a === b) return true;
  
    if (a && b && typeof a == 'object' && typeof b == 'object') {
      if (a.constructor !== b.constructor) return false;
  
      var length, i, keys;
      if (Array.isArray(a)) {
        length = a.length;
        if (length != b.length) return false;
        for (i = length; i-- !== 0;)
          if (!equal(a[i], b[i])) return false;
        return true;
      }
  
  
  
      if (a.constructor === RegExp) return a.source === b.source && a.flags === b.flags;
      if (a.valueOf !== Object.prototype.valueOf) return a.valueOf() === b.valueOf();
      if (a.toString !== Object.prototype.toString) return a.toString() === b.toString();
  
      keys = Object.keys(a);
      length = keys.length;
      if (length !== Object.keys(b).length) return false;
  
      for (i = length; i-- !== 0;)
        if (!Object.prototype.hasOwnProperty.call(b, keys[i])) return false;
  
      for (i = length; i-- !== 0;) {
        var key = keys[i];
  
        if (!equal(a[key], b[key])) return false;
      }
  
      return true;
    }
  
    // true if both NaN, false otherwise
    return a!==a && b!==b;
  }

  export default equal;